1. Field of the Invention
The invention is concerned with a fluid system of a vehicle which has a load response pump control and control valves that submit load signals back to the pump control in combination with standard control valves that are not load responsive. More particularly the invention is concerned with the addition of a load responsive control valve that allows the standard valves to respond as if they were load responsive. The system is particularly useful with outrigger hydraulic systems wherein the valves on the outrigger cylinder can be of the standard reversing type, and yet they can as a result of the present invention be used with a common variable displacement pump as is used for other systems of, for example, a mobile crane or the like.
2. Prior Art
Hydraulic fluid systems which utilize several valves each of which are load responsive, are known to the prior art. Basically such systems operate via a demand-compensated principle in which the pump discharge power from a variable displacement pump can be made proportional to the instantaneous load demand of one or more fluid motors powered by the pump.
Outrigger hydraulic systems are well known and are usable with mobile cranes and the like as for extending and retracting various hydraulic cylinders to position the outriggers. As is well known in the art, mobile crane outriggers conventionally serve to provide rigid ground support for cranes and the like during their use by appropriate extension and contraction of hydraulic cylinders located at the four corners of a vehicle. Generally each outrigger has a jack cylinder and a beam extension cylinder with appropriate fluid lines connected to each of the cylinders. Conventional reversing valves control the extension and contraction of each cylinder.
Vehicles having an outrigger system would generally include a variable displacement pump and would advantageously have a demand compensated hydraulic system, but such are not compatible with conventional outrigger hydraulic systems which use standard reversing valves. Also, it would significantly increase the cost and increase the complexity of the outrigger reversing valve system if the standard reversing valves were each to be replaced with a control valve that submitted a load signal back to the control of the variable displacement pump. The present invention is concerned with allowing the use of the same variable displacement pumping apparatus which operates, for example, an implement system of a mobile crane to operate the outrigger circuit. What results is demand-compensated hydraulic operation of the outrigger hydraulic system as a whole with a relatively low addition to the complexity of the valving and connections thereof and resulting in relatively low cost and trouble free operation.